It is known in the field of optical communications to use optical wavelengths as optical carriers for carrying digital or analog information. Also, the different wavelengths may be used to discriminate one set or channel of information from another. When a plurality of wavelengths are coupled or multiplexed onto a single fiber, this is called wavelength division multiplexing (WDM). Use of such WDM increases the overall bandwidth of the system. For example, a single fiber carrying two wavelengths has twice the bandwidth of a fiber carrying a single wavelength.
Also, high speed low-loss communication networks need wholly fiber optic networks as the transmission medium without converting to electronics along the communication path to minimize losses and maximize speed. Thus, the ability to switch optical signals at access nodes or between network rings, without converting from optical signals to electrical signals, and back again, i.e., provide an all- optical network, is desirable.
Currently there are several switch technologies that address these issues such as 1) acousto-optic tunable filters; 2) electro-optic tunable filters; and 3) liquid crystal Fabry-Perot filters. These techniques all work on the principle of polarization diversity which requires laser light to propagate through some birefringement material such as Lithium Niobate or polarization maintaining fiber. Such systems require careful polarization control and run the risk of distortion of the modulated optical signal due to polarization dispersion.
Also, existing wavelength division multiplexers which split the input light having two wavelengths on one fiber to two output fibers, each having one of the input wavelengths, are limited to only two outputs and the wavelengths must not be closely spaced together.
Therefore, it is desirable to have an optical all-fiber wavelength selective switch which guides input light having one or more wavelengths entirely through a communication grade single mode fiber.